Draw 3D gridlines below more important elements

Add mplot3d test to cover hiding most elements

mpl20 style on test images

Author: scottshambaugh

lib/matplotlib/tests/baseline_images/test_collections/polycollection_close.png

@@ -393,7 +393,7 @@ def test_EllipseCollection():
     ax.autoscale_view()
 
 
-@image_comparison(['polycollection_close.png'], remove_text=True)
+@image_comparison(['polycollection_close.png'], remove_text=True, style='mpl20')
 def test_polycollection_close():
     from mpl_toolkits.mplot3d import Axes3D  # type: ignore
 

lib/matplotlib/tests/baseline_images/test_figure/tightbbox_box_aspect.svg

@@ -476,7 +476,10 @@ def draw(self, renderer):
             # Draw panes first
             for axis in self._axis_map.values():
                 axis.draw_pane(renderer)
-            # Then axes
+            # Then gridlines
+            for axis in self._axis_map.values():
+                axis.draw_grid(renderer)
+            # Then axes, labels, text, and ticks
             for axis in self._axis_map.values():
                 axis.draw(renderer)
 

lib/matplotlib/tests/test_collections.py

@@ -445,26 +445,6 @@ def draw(self, renderer):
         self.offsetText.set_ha(align)
         self.offsetText.draw(renderer)
 
-        if self.axes._draw_grid and len(ticks):
-            # Grid points where the planes meet
-            xyz0 = np.tile(minmax, (len(ticks), 1))
-            xyz0[:, index] = [tick.get_loc() for tick in ticks]
-
-            # Grid lines go from the end of one plane through the plane
-            # intersection (at xyz0) to the end of the other plane.  The first
-            # point (0) differs along dimension index-2 and the last (2) along
-            # dimension index-1.
-            lines = np.stack([xyz0, xyz0, xyz0], axis=1)
-            lines[:, 0, index - 2] = maxmin[index - 2]
-            lines[:, 2, index - 1] = maxmin[index - 1]
-            self.gridlines.set_segments(lines)
-            gridinfo = info['grid']
-            self.gridlines.set_color(gridinfo['color'])
-            self.gridlines.set_linewidth(gridinfo['linewidth'])
-            self.gridlines.set_linestyle(gridinfo['linestyle'])
-            self.gridlines.do_3d_projection()
-            self.gridlines.draw(renderer)
-
         # Draw ticks:
         tickdir = self._get_tickdir()
         tickdelta = deltas[tickdir] if highs[tickdir] else -deltas[tickdir]
@@ -502,6 +482,45 @@ def draw(self, renderer):
         renderer.close_group('axis3d')
         self.stale = False
 
+    @artist.allow_rasterization
+    def draw_grid(self, renderer):
+        if not self.axes._draw_grid:
+            return
+
+        renderer.open_group("grid3d", gid=self.get_gid())
+
+        ticks = self._update_ticks()
+        if len(ticks):
+            # Get general axis information:
+            info = self._axinfo
+            index = info["i"]
+
+            mins, maxs, _, _, _, highs = self._get_coord_info(renderer)
+
+            minmax = np.where(highs, maxs, mins)
+            maxmin = np.where(~highs, maxs, mins)
+
+            # Grid points where the planes meet
+            xyz0 = np.tile(minmax, (len(ticks), 1))
+            xyz0[:, index] = [tick.get_loc() for tick in ticks]
+
+            # Grid lines go from the end of one plane through the plane
+            # intersection (at xyz0) to the end of the other plane.  The first
+            # point (0) differs along dimension index-2 and the last (2) along
+            # dimension index-1.
+            lines = np.stack([xyz0, xyz0, xyz0], axis=1)
+            lines[:, 0, index - 2] = maxmin[index - 2]
+            lines[:, 2, index - 1] = maxmin[index - 1]
+            self.gridlines.set_segments(lines)
+            gridinfo = info['grid']
+            self.gridlines.set_color(gridinfo['color'])
+            self.gridlines.set_linewidth(gridinfo['linewidth'])
+            self.gridlines.set_linestyle(gridinfo['linestyle'])
+            self.gridlines.do_3d_projection()
+            self.gridlines.draw(renderer)
+
+        renderer.close_group('grid3d')
+
     # TODO: Get this to work (more) properly when mplot3d supports the
     #       transforms framework.
     def get_tightbbox(self, renderer=None, *, for_layout_only=False):